Don't kid yourself. If Romney gets the nomination, his Mormonism will be front and center. What you have seen is just the opening rounds. In the general election, it will be far more vicious.
Reid's Mormonism is irrelevant. The Democrats would sacrifice one senator to win the White House in a heartbeat, particularly one who already has some ethical stain about him.
Mitt Romney will have a huge chore winning back the 10% or more of evangelicals who claim they won't vote for him in the general election. Without those voters, all the states that Dubya squeaked by in 2004 will be lost by Romney. The Democrats know this and will remind the evangelicals of why they don't want to vote for one of those "weird" Mormons. These arguments will also be effective on secular independents who Romney will have to attract if the evangelical vote abandons him.
I reject the premise that 10% or more Evangelicals will not vote for Romney, particularly in the face of Clinton. But, there will be few. My contention is that Romney’s crossover appeal - stemming mostly from his demonstrable family values - will dwarf that contingent.